'use strict'
let base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
let base64DecodeChars = new Array(
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
      52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
      -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
      15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
      -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
      41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1);
  //编码的方法
  function base64encode(str) {
      let out, i, len;
      let c1, c2, c3;
      len = str.length;
      i = 0;
      out = "";
      while(i < len) {
      c1 = str.charCodeAt(i++) & 0xff;
      if(i == len)
      {
          out += base64EncodeChars.charAt(c1 >> 2);
          out += base64EncodeChars.charAt((c1 & 0x3) << 4);
          out += "==";
          break;
      }
      c2 = str.charCodeAt(i++);
      if(i == len)
      {
          out += base64EncodeChars.charAt(c1 >> 2);
          out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4));
          out += base64EncodeChars.charAt((c2 & 0xF) << 2);
          out += "=";
          break;
      }
      c3 = str.charCodeAt(i++);
      out += base64EncodeChars.charAt(c1 >> 2);
      out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4));
      out += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >>6));
      out += base64EncodeChars.charAt(c3 & 0x3F);
      }
      return out;
  }
  //解码的方法
  function  base64decode(str) {
      var c1, c2, c3, c4;
      var i, len, out;
      len = str.length;
      i = 0;
      out = "";
      while(i < len) {

      do {
          c1 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
      } while(i < len && c1 == -1);
      if(c1 == -1)
          break;

      do {
          c2 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
      } while(i < len && c2 == -1);
      if(c2 == -1)
          break;
      out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));

      do {
          c3 = str.charCodeAt(i++) & 0xff;
          if(c3 == 61)
          return out;
          c3 = base64DecodeChars[c3];
      } while(i < len && c3 == -1);
      if(c3 == -1)
          break;
      out += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));

      do {
          c4 = str.charCodeAt(i++) & 0xff;
          if(c4 == 61)
          return out;
          c4 = base64DecodeChars[c4];
      } while(i < len && c4 == -1);
      if(c4 == -1)
          break;
      out += String.fromCharCode(((c3 & 0x03) << 6) | c4);
      }
      return out;
  }
  //16->8位转换
  function utf16to8(str) {
      var out, i, len, c;
      out = "";
      len = str.length;
      for(i = 0; i < len; i++) {
      c = str.charCodeAt(i);
      if ((c >= 0x0001) && (c <= 0x007F)) {
          out += str.charAt(i);
      } else if (c > 0x07FF) {
          out += String.fromCharCode(0xE0 | ((c >> 12) & 0x0F));
          out += String.fromCharCode(0x80 | ((c >>  6) & 0x3F));
          out += String.fromCharCode(0x80 | ((c >>  0) & 0x3F));
      } else {
          out += String.fromCharCode(0xC0 | ((c >>  6) & 0x1F));
          out += String.fromCharCode(0x80 | ((c >>  0) & 0x3F));
      }
      }
      return out;
  }
    //8->16位转换
  function utf8to16(str) {
      var out, i, len, c;
      var char2, char3;
      out = "";
      len = str.length;
      i = 0;
      while(i < len) {
      c = str.charCodeAt(i++);
      switch(c >> 4)
      {
        case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:
          // 0xxxxxxx
          out += str.charAt(i-1);
          break;
        case 12: case 13:
          // 110x xxxx   10xx xxxx
          char2 = str.charCodeAt(i++);
          out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F));
          break;
        case 14:
          // 1110 xxxx  10xx xxxx  10xx xxxx
          char2 = str.charCodeAt(i++);
          char3 = str.charCodeAt(i++);
          out += String.fromCharCode(((c & 0x0F) << 12) |
                         ((char2 & 0x3F) << 6) |
                         ((char3 & 0x3F) << 0));
          break;
      }
      }
      return out;
  }
  //编码
  export function Base64Encode(src){
    let  base64encodeString ;
      base64encodeString=  base64encode(utf16to8(src))
      return base64encodeString;
  }
  //解码
    export function Base64Decode(src){

      let base64encodeString;
       base64encodeString =  utf8to16(base64decode(src))
      return base64encodeString;
  }
